1. Field of the Invention
The present invention is directed to an apparatus and method for metering fluid. More particularly, the present invention is directed to an apparatus to injected a predetermined amount of a liquid into a fluid stream and methods for its use.
2. Description of the Prior Art
Several devices have been developed for injecting predetermined quantities of liquid additives into a liquid flow stream for such applications as adding medication to drinking water with additives such as chlorine or iodine and adding fertilizer concentrate to irrigation water. An exemplary device which is powered by the liquid stream to which the additive is being injected is described in U.S. Pat. Nos. 3,937,241 and 4,060,351 as issued to Philippe Cloup. In the apparatus described in the Cloup patents, the additive or adjuvant is injected into the main fluid stream within a piston chamber of a hydraulic motor which drives the additive injection pump.
The architecture for this metering pump, however, is disadvantageous when the additive is a corrosive fluid such as chlorine, fertilizer or other chemically active substance. Accordingly, it is desirable to be able to inject the additive into the liquid stream at a point downstream of the motor which is powering the additive pump to avoid problems associated with the corrosive action of the additive.
To accomplish this objective, a number of fluid pumps have been designed which inject the additive into the primary fluid stream where the primary fluid provides the motive fluid for activating the additive injection pump. Such a device is described for example in applicants"" U.S. Pat. No. 4,558,715 as issued to Walton.
While overcoming many of the disadvantages of prior fluid injection system, the apparatus described in the Walton patent involves a number of components which are subject to wear and subsequent failure. Elastic or elastomeric biasing components necessary in a piston drive pump are particularly prone to fatigue and failure. Moreover, the use of a piston and its auxiliary components enhance production and manufacturing costs.
The present invention addresses the above and other disadvantages of prior art metering pumps by providing a system which includes a minimum of moving components in a robust design to selectively inject a second and/or a third fluid in a fluid stream, where the second and third fluid constitute a predetermined percentage of the total mixture.
In one embodiment, the present invention is directed to an apparatus for generating a mixture of a first fluid and measured quantities of a second fluid, wherein the second fluid constitutes a predetermined percentage of the ultimate mixture. In one aspect, the system includes a flow meter which includes an inlet in fluid communication with the first fluid, a fluid outlet and first and second gears positioned between the outlet and inlet. The gears of the flow meter are meshed together and counter rotate relative to each other when the first fluid, e.g. water, is directed through the inlet to the outlet.
A shaft is connected coaxially to the first gear and the first gear of a cavity gear pump. The cavity gear pump includes a first and a second gear disposed in a housing and includes an inlet and an outlet. Each of the first and second gears define a transverse cavity or pocket to receive and pump a liquid from the inlet to the outlet. Because the first gear of the cavity pump is connected through the shaft to the first gear of the flow meter, a predetermined amount of the second fluid is pumped through the outlet of the cavity pump when a predetermined amount of the first fluid is directed through the flow meter.
In another aspect of the invention, a second shaft is coaxially coupled to the second gear of the flow meter and a first gear of a second cavity gear pump which also includes an inlet and an outlet where the inlet is coupled to a reservoir of a third fluid and the outlet is coupled to the fluid stream. In such a fashion, a third fluid may be selectively metered and introduced into the fluid stream.
The present invention offers a number of advantages over prior art metering pumps. One such advantage is a robust design which requires a minimum of moving components. In such a fashion, the apparatus is relatively inexpensive to manufacture and maintain.
Another advantage of the present invention is its lack of dependance on elastic biasing components to accomplish the metering process.
Another advantage is the ability to avoid contamination of the fresh water supply by introducing the metered additive concurrently with the metered water into the treatment pool. In such a fashion, inadvertent backflow will not result in a contamination of the water supply.
Yet other advantages include quiet operation, a compact size when compared to competitive devices and a low pressure loss across the inlet and outlet of the pump.